Electrical power systems employing generator sets powered by combustion engines, steam, or other means are well known installations used throughout the world. Such systems can include one or more generator sets whose purpose is to provide electrical power to a local power grid such as for a municipality or a factory, or much larger installations for powering entire cities. It is common for the generators to be coupled in parallel to an electrical power bus, which can often be connected to both a local power grid and a regional power grid. Regardless of scale, it is generally desirable to operate the electrical power system without interruptions in power and with as little disturbance as practicable.
When generators are connected for parallel operation it is common for one or more of the generators to operate in so-called droop mode such that load changes on an electrical power bus cause a speed and/or an output voltage of the generator to vary to a degree that can typically be selected by the operator, such as 5% droop, 10% droop, and so on. It is also typical for another generator in the same system to be operated in isochronous mode, such that frequency serves as the basis for control in response to load changes.
Engineers have experimented for decades as to how to best control speed, voltage, frequency, and other variables in the operation of paralleling generators. When load demands are relatively stable and consistent, generator speeds and power outputs will vary relatively little. Many electrical power systems are dynamic, however, as electrical loads are connected and disconnected. In installations where multiple substantially identical generator sets are used, controlling multiple generators during transient load changes or “transients” can be relatively straightforward as the response and behavior of the similarly situated machines is relatively predictable. Many systems nevertheless have a diversity of machines with, for example, multiple gas turbine engine powered generators from different manufacturers or having different designs and/or ratings, gas turbine powered generators in parallel with reciprocating engine powered generators, gas turbines with steam turbines, or still other combinations. In these less uniform systems additional complexity as to the control characteristics and responses of the different machines can be introduced. JP2014029736(A) to Kawabata Yasahara et al. is directed to an example reverse power flow controller that apparently limits instability of supply in certain electrical power systems.